Hazards: Tectonics/Volcanoes Flashcards
Name the layers of the earth
Crust
Mantle - lithosphere, asthenosphere
Outer core
Inner core
What elements make up the crust?
Very light elements... Silicon Oxygen Sodium Aluminium Potassium
Name the two types of crust
Continental
Oceanic
How thick is the continental crust?
30-70km thick
What is the continental crust made up of?
Granite
How thick is the oceanic crust?
6-10km thick
What is the oceanic crust made up of?
Basalt
Is continental or oceanic crust denser?
Oceanic
What is the mantle made up of?
Molten / semi molten rocks
What elements make up the mantle?
Light elements…
Silicon
Oxygen
What is the core made up of?
Dense iron / nickel alloys
Is the inner core solid or liquid?
Solid
Is the outer core solid or liquid?
Liquid
What temperature is the inner core?
> 5000°C
Where does the high temperatures in the core come from?
Primordial heat from the earth’s formation.
Radiogenic heat from radioactive decay of isotopes.
What consistency is the asthenosphere?
Semi molten
Where is the asthenosphere found?
Upper mantle - where convection is thought to occur
What is the lithosphere?
The solid layers of the earth
Where is the lithosphere found?
Crust and upper mantle
How thick is the lithosphere?
80-90km thick
How thick is the outer core?
2,200km
How thick is the inner core?
1,200km
Who developed plate tectonic theory? When?
Alfred Wegener, 1912
What was Alfred Wegener’s theory?
That a single continent existed 300million years ago - Pangea.
It area split into two continents - Laurasia (N), Gondwanaland (S).
Due to continental drift.
Give the geological evidence for Wegener’s theory of continental drift
- Appeared that S America and W Africa would fit together.
- Late Carboniferous glaciation (290million years ago) deposits found in S America, Antarctica and India.
- Striations on rocks in Brazil and W Africa which point to similar situation.
- Similar rock sequencing in N Scotland and E Canada.
Give the biological evidence for Wegener’s theory of continental drift
- Similar fossil brachiopods found in Indian limestone and Australia.
- Fossil remains of the Mesosaurus reptile are found in S America and S Africa.
- Fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica.
What couldn’t Wegener’s theory explain?
He couldn’t explain how the continents could move, so his ideas gained little ground
When was more evidence revealed to suggest that Wegener could have been correct?
1940s
What evidence discovered in the 1940s supported Wegener’s theory?
Mid Atlantic Ridge and ridge in Pacific Ocean were discovered.
The surrounding ocean crust was examined -> sea floor spreading.
Give the evidence for sea floor spreading
Iron particles in erupted lava are aligned with the earth’s magnetic field.
The earth’s polarity reverses every 400,000 years approx -> series of magnetic stripes with rocks aligned alternately.
The crust gets older the further away from the ridge it is = suggests the oceanic crust is slowly spreading away from this boundary.
Name all the Earth’s tectonic plates
Pacific Plate North American Plate Nazca Plate South American Plate African Plate Eurasian Plate Indo-Australian Plate
Which direction do plates move at a constructive boundary?
Plates move apart
What landforms/events are likely to occur at a constructive boundary?
Volcano - magma wells up to fill the gap and eventually a new crust is formed
Give a named example of a constructive boundary
Mid-Atlantic Ridge
Which direction do plates move at a destructive boundary?
Oceanic and continental plate move together.
Oceanic plate is denser so it subducts.
What landforms/events are likely to occur at a destructive boundary?
Volcano - friction causes oceanic plate to melt, magma rises through cracks and erupts.
Earthquakes - due to friction.
Give a named example of a destructive boundary
Nazca Plate is forced under South American Plate
Which direction do plates move at a collision boundary?
Two continental plates move together.
Neither is forced underneath the other so both are forced upwards.
What landforms/events are likely to occur at a collision boundary?
Fold mountains
Give named examples of a collision boundary
Himalayas
Rockies
Andes
Alps
Which direction do plates move at a conservative boundary?
Two plates slide past each other in opposite directions / same direction at different speeds.
What landforms/events are likely to occur at a conservative boundary?
Earthquakes - due to build up of friction leading to sudden movements.
Give a named example of a conservative boundary
San Andreas fault, California
Give an example of an oceanic ridge
Mid-Atlantic Ridge
Where do oceanic ridges form?
Constructive boundaries - magma rises
What landforms often occur along oceanic ridges?
Volcanoes, submarine volcanoes that may also rise above sea level.
Eg Surtsey, south of Iceland.
Give an example of a rift valley
East African Rift System
Where do rift valleys form?
Constructive boundaries - an area of linear shaped lowland is left between several highlands or mountain ranges when plates move apart.
Do rift valleys form on land or in oceans?
Can be found on land or in oceans due to sea floor spreading.
Give an example of a deep sea trench
Mariana Trench, west Pacific ocean
Where do deep sea/oceanic trenches form?
Destructive boundaries - where oceanic plate subducts.
At what depths are deep sea/oceanic trenches found?
7,300m - 11,000+m deep
Give an example of island arcs
Marianas Islands and Guam
What are island arcs?
Chains of volcanic islands that form parallel to oceanic trenches
Where do island arcs form?
Destructive boundaries - parallel to deep sea/oceanic trenches
Why do island arcs form?
When a plate subducts it melts due to friction/heat from the mantle -> magma is forced up through the overriding plate, forming a volcano.
When this occurs along an oceanic trench it forms a chain of volcanoes.
Give examples of young fold mountains
Rockies, Himalayas
Where do fold mountains form?
Collision boundaries - usually continental crusts
Define young fold mountain
Mountains formed 10-25million years ago
Define old fold mountain
Mountains that are >200million years old
Give examples of volcanoes
Calbuco, Chile (destructive boundary) Hawaiian Islands (hotspot chain)
Where do volcanoes form?
Constructive boundaries
Destructive boundaries
Hot spots
What is the generally accepted view on what causes plate movement?
That convection currents cause plate movement
Name the forces generated at plate boundaries that are thought to contribute to plate movement
Ridge push
Slab pull
What is ridge push?
Oceanic plates experience a force that acts away from the ridge - the result of gravity acting down the slope of the ridge.
What is slab pull?
Downward gravitational force that pulls the whole oceanic plate down - the result of the negative buoyancy of the plate.
Why is there thought to be some frictional resistance to ridge push?
Shallow earthquakes occur due to the repeated tearing apart of the newly formed crust - suggests frictional resistance.
Does the slab pull force lead to earthquakes?
Yes - due to friction created by pushing of the subducting plate against the overriding plate.
Why does the importance of driving/retarding forces vary from plate to plate?
Each plate moves at its own rate
How do hot spots form?
Radioactive decay within the Earth’s core generates very hot temperatures.
If the decay is concentrated, hotspots will form.
How do hot spots create volcanic activity?
Hot spots heat the lower mantle, creating localised thermal currents where magma plumes rise vertically.
The plumes can burn/melt through the lithosphere to create volcanic activity on the surface.
How do hot spots create a volcano chain?
The overlying plate moves over the stationary hot spot, resulting in a chain of active / extinct volcanoes in its path.
Give an example of a hot spot chain of volcanoes
Hawaiian Islands, Pacific Plate
Define hot spot
An area in the upper mantle where hot magma from the lower mantle upwells and melts through the crust.
How many islands are there in the Hawaiian chain?
8
Name the oldest Hawaiian island
Kauai - 5.5million years old
Name the youngest Hawaiian island
Hawaii - 0.7million years old
Give evidence for the Hawaiian islands being a result of hot spot volcanism
The islands get progressively older towards the northwest of the chain, with more being seamounts in this area.
Define seamount
A large underwater mountain of at least 1000m height above the sea floor.
Usually form when volcanoes age and sink.
Who came up with hot spot theory?
John Tuzo Wilson
What did J. Tuzo Wilson argue?
That volcanic regions like Hawaii could only exist if there was a localised source of heat beneath them:
Hot spots = thermal plumes.
Name the primary impacts of a volcanic eruption
Tephra
Pyroclastic flow
Lava flow
Volcanic gases
Define tephra
Solid material of varying grain size ranging from volcanic bombs to ash, all ejected into the atmosphere.
Define pyroclastic flow
Very hot, gas charged, high velocity flows made up of gas and tephra.
Give the speed and temperature of pyroclastic flow
800*C
700km/h
Give an example of an eruption that had an extreme impact by pyroclastic flow
Mt Vesuvius, Pompeii
Define lava flow
Stream of molten rock that pours from an erupting vent
Name the volcanic gases
Carbon dioxide Carbon monoxide Hydrogen sulphide Sulfur dioxide Chlorine
Give an example of an eruption that had an extreme impact by volcanic gases
Nyos, Cameroon, 1986
CO2 emissions killed 1700 people.
Name the secondary impacts of volcanic eruptions
Lahars Flooding Volcanic landslides Tsunamis Acid rain Climatic change
Define lahars
Combination of melted snow/ice and ash -> mud flows that move down the course of river valleys at high speeds.
Give an example of an eruption that had an extreme impact by lahars
Nevado del Ruiz, Colombia, 1985.
3/4 of the town of Armero were killed.
How can flooding result from an eruption?
When the eruption melts glaciers/ice caps.
Give an example of an eruption that caused extreme flooding
Grimsvotn, Iceland, 1996
Define volcanic landslide
Large masses of wet/dry rock and soil that fall, slide or flow very rapidly due to gravity.
Define tsunamis as a result of volcanoes
Sea waves generated by violent volcanic eruptions
Give an example of an eruption that led to a tsunami
Krakatoa, Indonesia, 1883.
Killed 36,000
Define acid rain
When gases eg sulphur combine with atmospheric moisture.
How can volcanic eruptions lead to climatic change?
The ejection of huge amounts of volcanic debris into the atmosphere can block the sun and reduce global temperatures.
Give an example of an eruption that led to climatic change
Mt Pinatubo, Phillipines, 1991
By what means can people manage volcanic hazards?
Prediction
Mitigation - preparation, prevention, adaptation
Is it easy/difficult to predict when a volcano will erupt?
Difficult
How can the effects of volcanoes be managed by prediction?
Monitoring of ground deformation (swelling).
Changes in groundwater levels / chemical composition of gwater.
Changes in gas emissions -> higher sulphur = closer eruption.
Monitoring seismic activity using seismometers.
Monitoring temperature change using thermal imaging/ satellite cameras.
Give an example of when prediction of a volcanic hazard was effective
Popocatepetl, Mexico, 2000.
Use of seismology saved 30,000 people.
Name the means of mitigation of a volcanic hazard
Preparation
Prevention
Adaptation
How can the effects of volcanoes be managed by mitigation: preparation ?
Exclusion zones around the volcano. Evacuation. Emergency supplies of basic provisions. Having funds available to deal with aftermath. Good communication system -> warning. Emergency shelters. Hazard maps showing predicted pathway of eruption. Educating residents of what to do.
How can the effects of volcanoes be managed by mitigation: prevention ?
Prepared with evacuation routes.
Development of a warning system that detects seismology etc.
Building structures that are able to withstand eruptions.
Lava channels to redirect flows.
Building infrastructure away from danger zones.
How can the effects of volcanoes be managed by mitigation: adaptation ?
Developing new monitoring systems.
Amendment to eruption plans based on past experience.
Modification to prevention methods based on past experience.
Residents may choose to relocate.
